Compared to control muscle, autografts are low in oxidative capacity, small in functional cross-sectional area, and low in maximal blood flow. Consequently, autografts are more easily fatigued and are unable to develop as much absolute isometric tension as control muscle. Endurance exercise conditioning increases oxidative capacity and strength conditioning increases functional cross-sectional area of non-transplanted muscle. The overall aim of this project is to determine the capability of physical conditioning to improve the structure and function of autografts. The soleus muscle will be auto-transplanted in rats, and animals will be assigned to one of three groups: no exercise, 1 hours running at 1.0 mph on 15% slope, and 1 hour running at 1.0 mph on 30% slope. Animals will be sacrificed following selected intervals of conditioning, and functional and structural variables of the autografts will be assessed. Variables include: oxidative capacity; histochemical demonstration of myofibrillar ATPase, succinic acid dehydrogenase, capillarity, and hematoxylin and eosin; and contractile properties. Hypotheses will be tested regarding the response of autografts to cessation of physical conditioning. This project will provide basic information on the time course, magnitude and mechanism of adaptation of autografts. Furthermore, this project likely will yield useful data for protocols for the physical conditioning of humans following the clinical application of free whole skeletal muscle transplantations.